1. Field of the Invention
This invention relates to a semiconductor structure in which an epitaxial semiconductor layer is used to electrically passivate and insulate the semiconductor on which it is deposited. Particularly, this invention relates to a semiconductor structure wherein the passivating/insulating layer is a composition of the general formula Zn.sub.1-x-y M.sub.X Q.sub.y Se:D 0.ltoreq.x23 1; 0.ltoreq.y.ltoreq.1, M and Q are different selected elements and D is a dopant for ZnSe.
2. Description of the Prior Art
In today's world, developments in electronic devices demand faster and faster reaction speed. As noted by D. L. Lile in a review article entitled "Dielectric Layers for Device Applications on III-V Compounds-An Assessment," Insulating Films on Semiconductors, Simonne & Buxo (editors), Elsevier Science Publishers, Holland, pp. 57-63 (1986), work on improving electronic devices has been driven by the "requirements of increased data processing rates and has taken a variety of forms including ...the use of "high velocity" materials and novel device structures such as the HEMT in AlGaAs/GaAs to increase the rate of information transfer. Such structures have typically been proposed on the III-V semiconductor compounds because it is this class of materials which has in the general both the required high velocity carriers, the correct band gap for operation at room temperature and a structure that allows for a variety of intermixed and crystallographically compatible materials combinations."
Lile states that "to fully utilize these compound semiconductors however it is of some importance that appropriate dielectrics be available to provide for passivation, crossover isolation and active gate insulation. To date, efforts to develop such insulators for III-V semiconductors have met with only limited success".
Lile further notes on page 58 that "Passivation, even on the most widely studied III-V compound GaAs... is less than a fully developed process which needs solution, even if non-insulated gate active device structures are retained. Clearly, bipolar circuits as we now know them on Si would be impossible in the absence of good SiO.sub.2 layers and likewise a GaAs MESFET technology also will require good passivation to fully meet its performance expectations."
Thus, as Lile notes above, the art has yet to develop a suitable passivating or insulating layer for III-V compounds which functions as effectively as silicon dioxide does in silicon-based semiconductors.
Several techniques have been developed to "work around" the absence of an effective passivation layer. The techniques used are described by Lile in his assessment, and in an earlier review article by H. H. Wieder, "Device Physics and Technology of III-V Compounds". J. Vac. Sci. Technol. A2(2), pages 97-102, Apr-June (1984)
Wieder discusses the problems in creating effective transistors with III-V compound semiconductors, particularly gallium-based semiconductors such as gallium arsenide (GaAs). To date, the materials proposed and tried as insulating layers for III-V compound semiconductor devices have not been satisfactory. These insulators do not result in the development of the full potential of III-V compound semiconductors devices.
The insulating materials applied to date have been applied by several techniques including vapor phase deposition, epitaxial crystal growth, pyrolisis etc. The techniques are all well documented in the art.
Several substances and techniques for the passivation have been described and claimed in the patent literature. Shuskus, in U.S. Pat. No. 4,545,572, describes a phosphorous-nitrogen based glass for use as a passivation layer on III-V semiconductor materials. Hodgson et al. describe a zinc-suplhide capping layer for gallium-arsenide devices in U.S. Pat. No. 4,354,198. Pancholy et al. describe a thermally deposited arsenic-oxide layer as a surface passivation method in U.S. Pat. No. 4,302,278 and Teherani et al. describe passivating Hg.sub.1-x Cd.sub.x Te substrates with CdSe or HgSe.
In recent years, research has been conducted to make and study a series of compounds known generally as diluted magnetic semiconductors (DMS) or semimagnetic semiconductors. These DMS compounds are ternary or quaternary semiconducting compounds whose lattice is partly made up of substitutional magnetic ions. The majority of DMS's incorporate a magnetic ion, usually mangansee, into II-VI semiconducting hosts, particularly chalcogenides.
The properties of these DMS alloys and crystals of these alloys have been discussed in several review articles including, "Diluted Magnetic Semiconductors: An Interface of Semiconductor Physics and Magnetism", Furdyna, J. Appl. Phys. 53(11), pp. 7637-7643, Nov. (1982); "Effect of Fe on the Carrier Instability in HgSe", Vaziri et al, Appl. Phys. Lett. 47(4), pp. 407-409, Aug 15, 1985; "Diluted Magnetic Semiconductors: Issues and Opportunities", Furdyna, J. Vac. Sci. Technol A(4) (1986), pp. 2002-2009; "Bonding and Stability in Narrow-Gap Ternary Semiconductors for Infrared Applications", Wall et al., J. Vac. Sci. Technol A(4), pp. 2020-2013, Jul/Aug (1986); "Reduction of Charge-Center Scattering Rate in Hg.sub.1-x FexSe", Pool et al., Physical Review B, Vol. 35, pp. 3900-3909, Mar. 15, 1987-I; "Band Structure and Electronic Properties of Mercury Chalcogenide Alloys Containing Iron", Reifenberger et al., J. Vac. Sci. Techol. A5(5), pp. 2995-3002, Sept/Oct (1987).
Each of these articles discusses the properties of DMS alloys and speculates that the alloys should ultimately find application in devices. For example, Reifenberger et al., J. Vac. Sci. Technol., Vol. 5(5) at p. 3001 last paragraph states with respect to mercury compounds: "Because of the expected increase in the stability of the electron concentration in the materials, they may ultimately be attractive from the device application point of view." In each of the articles discussing iron-containing DMS's, the researchers found markedly improved results and greater stability then in the Mn-based counterparts.
The inventors and a co-worker reported a study of the properties of an epitaxial layer of Zn.sub.1-x Fe.sub.x Se on GaAs in an article entitled "Molecular Beam Epitaxial Growth and Characterization of the Diluted Magnetic Semiconductor Zn.sub.1-x Fe.sub.X Se", Jonker et al., Appl. Phys. Lett 50(13), pp. 848-850, Mar. 30, 1987. An abstract of a related paper was published earlier in March. The abstract is entitled "MBE Growth and Characterization of Zn.sub.1-x Fe.sub.x Se", Jonker, et al., Bull. Amer. Physical Soc. Vol. 32(3), p. 810, March (1987). The articles do not report application of these structures as devices.